In the coating of workpieces such as metal substrates, chemical conversion treatments have been conventionally performed on the surfaces of the metal substrates by using various chemical conversion treatment agents in order to form chemical conversion coating films on the surfaces of the metal substrates and thereby secure the adhesion of coat films and corrosion resistance. A known example of the chemical conversion treatments is the chromate chemical conversion treatment using a chemical conversion treatment agent (a chromic acid salt or the like) containing chromium. However, it has been pointed out that the chromate chemical conversion treatment is hazardous because of chromium. Moreover, another known example of the chemical conversion treatments is a chemical conversion treatment using a chemical conversion treatment agent containing a so-called zinc phosphate. However, the chemical conversion treatment agent containing zinc phosphate has a high metal ion concentration and a high acid concentration and is extremely highly reactive, in general. Hence, the chemical conversion treatment using the chemical conversion treatment agent containing zinc phosphate has a problem of requiring wastewater treatment. In addition, the chemical conversion treatment using a chemical conversion treatment agent containing zinc phosphate also has a problem that deposit called sludge is formed due to formation of water-insoluble salts, and that a removal and disposal of the sludge is necessary. As described above, the chemical conversion treatment using a chemical conversion treatment agent containing zinc phosphate has problems in terms of economical efficiency and workability. For this reason, studies are being made recently on chemical conversion treatments using chemical conversion treatment agents other than the chemical conversion treatments agent containing chromium and the chemical conversion treatment agent containing zinc phosphate.
For example, Japanese Unexamined Patent Application Publication No. 2007-262577 (PTL 1) discloses a chemical conversion treatment agent containing a zirconium compound and/or a titanium compound and an organosiloxane. Moreover, PTL 1 shows examples of the organosiloxane such as a co-condensate of 3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane (described in Example 6 in PTL 1) and a co-condensate of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane (described in Example 17 of PTL 1). However, conventional chemical conversion treatment agents as described in PTL 1 are not necessarily sufficient in terms of coat film adhesion.